Deep Space 9 was initially put on a three-shift rotation when the Federation took over its administration, but this changed in 2372 due to innovations by MajorKira Nerys. Kira first revealed her plans to CaptainBenjamin Sisko when he was seriously injured. She'd hoped that discussing station business might keep him conscious. Later, after he'd recovered, Sisko decided to put the station on a four-shift rotation, saying that the idea had "occurred" to him. He thought the crew "might appreciate more flexibility in their schedules". (DS9: "Starship Down") The concept went through a probationary period until it was finally made permanent because, as Kira put it, there were "less mistakes due to fatigue". (DS9: "Accession")

The day shift or day watch is the first duty period which theoretically happens during whatever would be considered day in space. It takes its roots from day shifts currently in use in military and other jobs. The day shift would presumably be followed by the night watch, which was a time of limited activity. (TNG: "Data's Day", "Lessons")

Usually this would be the time when the senior officers were on duty, though senior officers throughout all the series were often at work beyond the boundaries of their shifts.

In one episode (TNG: "Data's Day") Riker relieved Commander Data who had been in charge of the night shift on the Enterprise-D. Riker stepped out of the turbolift with a duty crew that didn't include any senior officers.

The night shift is a duty period that occurs during the hours in which an officer would otherwise be sleeping. It is usually relegated to the junior officers, as most people are not fond of the night shift. Aboard starships and space stations, however, there is technically no such thing as "night" or "day". The night shift is preceded by the swing shift. (DS9: "The Assignment")

Alpha shift was a duty shift aboard the USS Enterprise-A and the USS Enterprise-D, the first shift of the day watch. Aboard the Enterprise-A, the shift began at 0800 and ended at 1600 hours. Aboard the Enterprise-D, it ended at 1200 hours.

LieutenantMcDowell was part of the gamma shift on board the ship soon after, until Captain Edward Jellico ordered to rearrange the duty shifts and let the new delta shift replace the gamma shift. (TNG: "Chain of Command, Part II")

In 2370, during a training simulation, Commander Riker informed the alpha shift, including Lieutenant Commander Data, and the ensigns Sito Jaxa and Sam Lavelle, that their response time was seven percent slower that the response time of the gamma shift. (TNG: "Lower Decks")